The invention relates to oscillation radiography cameras.
A radiograph is "a picture produced on a sensitive surface by a form of radiation other than light." [Webster's Ninth New Collegiate Dictionary] For instance, a radiograph is typically "an X-ray or gamma ray photograph," [ibid.] but radiographs can also be made by corpuscular neutron or beta radiation. In either case, whether the radiation is composed of bosons, like photons and nuclei with an even number of nucleons, or composed of fermions, like neutrons, protons, other nuclei with an odd number of nucleons, electrons and positrons, the beam can always be completely characterized by appropriate quantum effects. The sensitive surface on which the radiograph picture is produced can include suitable electronic detector sensor arrays and charge-coupled devices (CCDs) as well as the more usual plates treated with photographic emulsions. Radiography is "the art, act, or process of making radiographs." [ibid.]
When a beam of X-rays or other energetic rays reaches certain material which is transparent to that particular type of beam, it simply goes through that material. Some other material may however, under some conditions, scatter the beam into one or more directions different from the incident beam. This phenomenon of scattering can be utilized to investigate the characteristics of the beam or of the material. In such scattering experiments the goal is to determine how the beam is scattered into the various directions. One method to achieve this goal is to place a photographic film behind the sample of the material such that a picture of the scattered pattern is produced. Since some rays in the beam may pass directly through the film, it is desirable to use a stack of more than one film in order to record all of the rays. In any case, the picture(s) can be inspected either visually or by automatic film scanners via a computer to determine the various aspects of the scattering.
There are several types of cameras known in the radiography art which are designed to measure scattering as discussed above. An oscillation radiography camera is one of several types of radiography cameras distinguished by the manner of moving the sample exposed to the radiation and the detectors of the radiation scattered by the sample. These are discussed generally by Arndt et al., J. Applied Crystallography 6:457, 1973. For example, an oscillation camera rotates the sample, to a small extent (which depends on the specific sample being radiographed, but generally is in the range of from around 0.5.degree. up to around 2.degree.), back and forth in an oscillatory fashion, about a fixed axis, during exposure of the sample to the radiation. A rotation camera rotates the sample, to a larger extent (which also depends on the specific sample being radiographed, but generally is in a range greater than or equal to around ten times the range for oscillation cameras, i.e. from around 5.degree. to around 20.degree. or more), back or forth, about a fixed axis, during exposure of the sample to the radiation.
Stout and Jensen, In X-ray Structure Determination, Macmillan Publ. Co. Inc. 98, 1968 generally describe a precession camera which precesses the sample around in the beam of radiation. Stout and Jensen also describe a Weissenberg camera (at page 83) which also causes movement of the sample exposed to the radiation. Both the precession and Weissenberg cameras cause movement of the sample being exposed and, during such exposure, movement of the detectors recording the scattered beam.
Oscillation cameras, such as those made by Charles Supper Co. of Natick, Mass., and Enraf-Nonius in Europe, conventionally use a single motor to oscillate the sample about an axis perpendicular to the beam. A combination camera made by Charles Supper Co. of Natick, Mass., combines two motors, one to effect oscillation, and the other to effect precession. The motors are not used simultaneously; the oscillation exposures are taken while the precession motion is disabled, and the precession exposures are taken while the oscillation motion is disabled.